I.QUESTIONS AND ANSWERS

A.FLUID CATALYTIC CRACKING/a.PROCESS(Contd.)

Q2.For FCC units with a closed riser termination device(RTD)/cyclone systems,do you operate with the primary separator sealed or unsealed in the stripper bed? What differences in performance do you see between these modes?Which do you prefer?

The choice between sealed and unsealed operation is often dictated by the hardware design,sincesome units can only operate in one mode.For those that can operate either way,the choice is usually dictated by either dry gas make or catalyst losses.One unit starts up unsealed and switches to sealed mode when the unit operation stabilizes.

I. QUESTIONS AND ANSWERS

A. FLUID CATALYTIC CRACKING

a.PROCESS

Q1-.What  process or catalyst options are available for shifting  yield selectivity's from gasoline to distillate while minimizing the impact on light olefin yields?

How are the product properties impacted?

How does change-out rate impact the viability of the catalyst options?

A1-The suggested process options for maximizing distillate and light olefin yields are as follows:

Gasoline can be undercut,with the heavier portion dropped to distillate.Cat:oil can be reduced to reduce conversion of distillate to gasoline,which will also increase the olefinicity of the C4s.Reducing cat:oil will increase HCO relative to LCO.

The suggested catalytic options for maximising distillate and light olefin yields are as follows:

Catalytic surface area can be increased to maximize conversion to LCO while minimizing bottoms.This will reduce Gasoline yield relative to LCO while maintaining or increasing olefin yield.A bottoms cracking additive can be used as a quicker way to achieve this effect.The downside to increased matrix surface area is increased coke make.ZSM-5 can be used to increase light olefins at the expense of  gasoline.This option has the advantage of quick response but it needs to  be used in conjuction with process changes to increase  distillate yield.. Catalyst zeolite content can be decreased to minimize cracking of  ddistillate to gasoline.Zeolite rare earth can be optimised to enhance LCO  quality.Decreasing rare earth decreases hydrogen transfer from LCO to gasoline and light olefins and improves LCO product quality.Rare earth changes as well as other catalyst modifications,need catalyst testing to verify the optimum.

There is not much potential for making distillate when processing very paraffinic or heavily hydrotreated feed,since the conversion tends to be high,and gasoline and light olefins are favoured over distillates.